The aim of the present invention is to provide a catheter with a puncturing cannula which may be removed from the catheter without risk of injury for the patient and the nursing staff nor risk of damaging the equipment and whose tip is protected before as well as after puncturing the body cavity. According to the invention this object is satisfied by a catheter with removable cannula (1) for puncturing a body cavity whereas the catheter can be moved freely in the longitudinal direction in the cannula (1). The cannula is characterised in that it is tubular in shape and provided with a longitudinal slot (10) extending over 45° to 180° of the circumference of the cannula (1) and in that it is provided in a tubular sheath (2) so that they can be displaced in the longitudinal direction inside said tubular sheath (2).
